Not a good thing to do. Attachments points are different, floorpan is different, towing capacity is different, maximum loads and chassis stresses catered for are different.

Basically this would in my view be a waste of time, and potentially dangerous. Towbars are usually specific in their vehicle application and should never be messed about with.

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Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
Current: 2012 R80 Countryman SDX Green/Cream